Television apparatus



Patented Feb. 27, 1940 PATENT OFFICE TLVISION APPARATUS Erch Schwartzand Ernst Ruska, Berlin-Zchlen- (1 1, Germany. ass g o s to the firmFernseh Aktiengesellschafi, Germany Zelflenflorf, near Berlin,

Application November 6, 1936, Serial No. 109,576 In Germany November 9,1935 Claims.

The present invention relates to an arrangement which permits combiningan image analyzer with an electron multiplier. Such a. combination is ofimportance since the image analyzer does not fulfill those exactaccumulator requirements which it is theoretically supposed to fulfill,and since the subsequently necessary amplification of the image analyzersignals is preferably efiected in an amplifier of which the first stagesare as free as possible from crackling tube noises which at most areequal to those of the image analyzer per se. Such amplifiers, free f1omcrackling tube noises, are usually operated by means of electronmultiplier arrangements.

' The combination of image analyzer and multiplier is difficult tosecure because the signal currents of the image analyzer fiowing asdisplacer ment currents in the conductor must again be converted intofree electron currents in order to be able to engender the secondaryemission eect in the electron multiplier. The conversion of galvanicconduction currents into currents of free electrons by means of electricglow discharges is not serviceable in this connection because theincandescent cathode required positively introduces a screen efiect. Afurther difliculty resides in the fact that the free electron currentswhich are set free by the signal currents of the image analyzer must bedirected towards a small surface, the inlet point of the electronmultiplier.

In accordance with the invention a tube is attached to the imageanalyzer, which tube contains a photo-cathode of which the emission iscontrolled by the signal currents of the image analyzer. Suchphoto-cathodes, as is well known, have a smaller crackling tube noiseeffect than incandescent cathodes. The electrons emanating from thisphoto-cathode are multiplied in an attached multiplying tube. Thephoto-cathode which is energized by a constant light source may be ofpoint-like type and may be delineated on a diaphragm by an electronlens, the said diaphragm forming the inlet opening for the multip ier,or it may be disposed directly in the vicinity of this inlet opening.Any radiation of desired wave length may be used for energizing thephoto-cathode, 9. g. even Roentgen ray radiation.

Embodiments of the invention are schematically illustrated in thedrawing wherein:

Fig. 1 shows the combination of an image analyzer With a multiplier.

Fig. 2 illustrates a further embodiment of the multiplier.

Fig. 3 shows a tube which combines the image analyzer and the multiplierin one housing.

In Fig. 1, A indicates an image analyzer of ordinary construction, B isthe discharge tube of the invention, whereas C represents the electronmultiplier which is combined With the discharle tube B to form a singlevacuum tube.

The image analyzer comprises an anode I and a photo-electric mosaic 2from which the displacement currents flow to signal plate 3 and thenceacross resistance 4 back to battery 5. Whereas normally the voltage dropin resistance a is coupled to an ordinary amplifier tube, in accordancewith the present invention the voltage drop is applied across resistanoe4 to the Wehnelt cylinder l8 and the cathode 6 of the discharge tube B.The cathode 5 is not, as customary, activated to produce thermionicelectron emission, but is provided with a coating of caesium or otheralkali earth metal. The cathode is energized to the emitting point bymeans of a constant light source 8 which is projected by a lens 9 andmirror l0 onto cathode 6. The mirror may be located in vacuo andfastened to one of the electrodes of the discharge tube B. The electronlens, which is here indicated as a magnetic collector coil l, delineatesthe cathode 6 on the anode diaphragm M. Behind the diaphragm l4 there isdisposed an electron multiplier of known type. Such a multiplier isshown and described in detail in the Philo T. Farnsworth Patents Nos.2,071,515 and 2,071,517, issued February 23, 1937. In these patentsthere is shown a method of causing an electron cloud to oscillate backand forth between two secondarily emissive cathodes, producing anamplified stream at each impact on the cathodes, and being focusedduring successive passages by a magnetic focusing coil. After eachimpact. the electron cloud is accelerated toward the opposite cathode bya charge on a cylindrical accelerating anode placed midway of thecathodes. and the final velocity before each cathode impact suificientto produce secondaries is insured by an alternating potential built upon cathodes themselves through a resonant circuit connecting them, asdescribed in detail in the patents referred to above. In the figures,the secondarily emissive cathodes are represented by the electrodes Iland l2 and the accelerating anode by the annular electrode I3. Thephoto-'- cathode 6, the saturation current of which is determined by theluminosity of the light source 8, emits an electron current which ismodulated by the signal voltage at the Wehnelt cylinder I8.

This varies the number of primary electrons shot into the multiplier.

In accordance with Fig. 2 the electrons which emanate from thephoto-cathode are not gath ered by a. separate collectr coil and shotinto the multiplier, but they issue through an opening 14 directly intothe space between the electrodes H and [2. The control is efiected by agrid I which is used in lieu of the Wehnelt cylinder [8 of Fig. 1.

In Fig. 3, the image analyzer is combined with the multiplier into onehousng l6. The optical image is thrown on the moSaic surface 2, to themetallic rear side 3 of which the cathode 8 is attached. The resistance4 may likewise'be disposed inside the tube between the cathode 3 andWehnelt cylinder 18. The electron ray produced by cathode 6 passesthrough diaphragm l4 into the multiplier, as shown in Fig. 1. The entiretube may be disposed inside a common collecter coil ll adapted toproduce an image of the cathode 6 and the cathode of the image analyzerin the ratio of 1:1.

We claim:

1. In combination with a dissector and an alternating currentmultiplier, means for energizing said multiplier from said dissectcrcomprising a photo-enfissive cathode axially alined with saidmultiplier, means for constantly illuminating said cathode, a Wehneltcylinder disposed about said cathode, an entry port to said multiplierin registry with said cathode, and means for energizing said Wehneltcylinder from the output of said dissector.

2. In combination with a dissector and a multiplier having an envelopeenclosng two opposed cathodes and a cylindrical anode intermediatethereof positioned symmetrically about the axis of said envelope, meansfor utilizing the output of said dissector to control said multiplier,comprising a photo-cathode disposed in said envelope in axial alinementwith said multiplier cathodes, a beam aperture formed through one ofsaid cathodes alined with said photo-cathode, means for directing aconstant intensity light upon said said enVel0pe alined with saidaperture, a control electrode disposed about said photoemisslve cathode,an external source et constant intensity light, means for focusing suchlight* upon said photo-cathode, means for focusing photoemssien fromsaid photo-cathode upon said. multiplier cathode aperture, and means forleading a signal potential to said control electrode.

4. An evacuated cylindrlcal insulating envelope, an image dissectordisposed within one and of said envelope, an alternating currentmultiplier adapted to be energized by photoemissicn disposed within theopposite and there0f, an apertured entrance to said multiplier, aphoto-cathode disposed between said dissector and multiplier in registrywith said apertured entrance, an external source of constant intensitylight, means for focusing light thereirom upon said photo-cathode, acontrol electrode about said photo-cathode, means for energlzng saidcontrolelectrode from said dissector, and means for Iocusing emissionfrom said photo-cathode upon said apertured multiplier entrance.

5. In combination, an electron multiplier, a photo-cathode, means forcontinucusly energiz ing said photo-cathode to the point of emissicn ofelectrons, means for guiding electrons from said photo-cathode to saidelectron multiplier, and means for modulating the flow of electrons tosaid electron multiplier in accordance with signals.

ERNST RUSKA ERCH SCHWARTZ.

